coal seam

Coal seam fire

A coal seam fire or mine fire is the underground smouldering of a coal deposit, often a coal mine. Such fires have economic, social and ecological impact.

Coal fires can burn for very long periods of time (from months to centuries), until the seam in which they smoulder is exhausted. They propagate in a creeping fashion along mines shafts and cracks. Because they are underground, they are extremely difficult and costly to reach and extinguish. There is a strong similarity between coal fires and peat fires.

Origins

Mine fires may begin as a result of an industrial accident, generally involving a gas explosion. Historically, some mine fires were started when bootleg mining was stopped by authorities, usually by blowing the mine up. Many recent mine fires have started from people burning trash in a landfill that was in proximity to abandoned coal mines, including the much publicized Centralia, Pennsylvania fire, which has been burning since 1962. Of the hundreds of mine fires in the United States burning today, most are found in the state of Pennsylvania.

Some fires along coal seams are natural occurrences. Some coals may self-ignite at temperatures as low as 40 °C (104 °F) in the right conditions of moisture and grain size.
Wildfires (lightning-caused or others) can ignite the coal closer to the surface or entrance, and the smouldering fire can spread through the seam, creating subsidence that may open further seams to oxygen and spawn future wildfires when the fire breaks to the surface. Prehistoric clinker outcrops in the American West are the result of prehistoric coal fires that left a residue that resists erosion better than the matrix, leaving buttes and mesa. It is estimated that Australia's Burning Mountain, the oldest known coal fire, has burned for 6,000 years.

Globally, thousands of inextinguishable mine fires are burning, especially in China and India, where poverty, lack of government regulations and runaway development combine to create an environmental disaster. Modern strip mining exposes smoldering coal seams to the air, revitalizing the flames.

Rural Chinese in coal-bearing regions often dig coal for household use, abandoning the pits when they become unworkably deep, leaving highly combustible coal dust exposed to the air. Using satellite imagery to map China's coal fires resulted in the discovery of many previously unknown fires. The oldest coal fire in China is in Baijigou and is said to have been burning since the Qing Dynasty.

Detection

Infrared detecting equipment is able to track the fire's location as the fire heats the ground on all sides of it.

Environmental impact

Besides destruction of the affected areas, coal fires emit gases that may contribute to global warming.
China's coal fires, which consume an estimated 20 – 200 million tons of coal a year, make up as much as 1 percent of the global carbon dioxide emissions from fossil fuels.

Extinguishing coal fires

The task of extinguishing underground coal fires, sometimes exceeding temperatures of 540 °C (1,000 °F), is both highly dangerous and very expensive.

In 2004, the Chinese government claimed success in extinguishing a mine fire at a colliery near Urumqi in China's Xinjiang province that had been burning since 1874. However, a March 2008 Time magazine article quotes researcher Steven Q. Andrews as saying, "I decided to go to see how it was extinguished, and flames were visible and the entire thing was still burning.... They said it was put out, and who is to say otherwise?"